Physical Activity Trends --- United States, 1990--1998

Physical activity is associated with numerous health benefits
(1), and increased participation in various types of leisure-time physical activity had been
encouraged during the 1990s (2). To determine national estimates of leisure-time physical
activity during 1990--1998, data were obtained from the Behavioral Risk Factor
Surveillance System (BRFSS). This report summarizes the results of that analysis, which
indicate that leisure-time physical activity trends have remained unchanged.

BRFSS is a population-based, random-digit--dialed telephone survey of the
civilian, noninstitutionalized U.S. population aged
>18 years. Forty-three states and the
District of Columbia collected data about physical activity for 1990, 1991, 1992, 1994,
1996, and 1998. Data were not collected by all states during 1993, 1995, and
1997. Respondents were asked about the two physical activities or exercises they engage
in most often and about the frequency, duration, and distance (as appropriate) of
each activity. Responses were then classified as one of 56 selected activities (Table 1). Moderate activity was defined as any of the 56 selected activities, and
vigorous activity was defined as aerobic physical activity classified as vigorous-intensity
based on estimated metabolic expenditure (MET) (Table 1). To classify an activity as
vigorous, it must be aerobic with an assigned MET value
(3) that is at least 60% of a person's maximal cardiorespiratory capacity (MCC). MET values are determined using
two regression equations for MCC (4): one for men (METS
60%MCC = [0.6 x (60 - 0.55 x age)]/ 3.5) and one for women (METS
60%MCC = [0.6 x (48 - 0.37 x age)]/ 3.5).

To have achieved recommended levels of physical activity, a person must
have reported engaging in moderate-intensity physical activity
>5 times per week for >30 minutes each time, vigorous-intensity physical activity
>3 times per week for >20 minutes each time, or both during the preceding month. Persons reporting
some activity during the preceding month but not enough to be classified as moderate
or vigorous were classified as insufficient. Persons classified as inactive reported
no physical activity outside of their occupation during the preceding month. Data
were analyzed using SUDAAN to obtain prevalence estimates for recommended levels
of physical activity. All data were age adjusted to the 2000 standard population.

The prevalence of those who engaged in recommended levels of activity
increased slightly from 24.3% in 1990 to 25.4% in 1998, and the prevalence of those
reporting insufficient activity increased from 45.0% in 1990 to 45.9% in 1998 (Figure 1).
Those reporting no physical activity decreased from 30.7% in 1990 to 28.7% in 1998.
The components of recommended activity remained relatively stable (Figure 2).

Reported by: Physical Activity and Health Br, Div of Nutrition and Physical Activity,
and
Cardiovascular Health Br, Div of Adult and Community Health, National Center for
Chronic Disease Prevention and Health Promotion; and an EIS Officer, CDC.

Editorial Note:

The findings in this report indicate that trends in physical
activity remained stable during 1990--1998. Classifying persons according to their main
pair of nonoccupational activities during the preceding month suggests that
only approximately one fourth of U.S. adults meet recommended levels of
physical activity.

During 1990--1998, the BRFSS formula for calculating vigorous intensity
changed. In 1992, vigorous intensity was calculated as 50% of MCC; before 1992, it
was calculated as 60% of MCC, the generally accepted threshold for vigorous activity.
The data reported here vary from previous reports
(1) because all years of data were calculated using the same formula for vigorous intensity (60% MCC). Therefore,
the slight increase in vigorous physical activity that might have appeared after 1992
in previous reports was attributed to differences in calculating vigorous physical
activity rather than an actual increase among the population.

The findings in this report are subject to at least four limitations. First, these
data are self-reported and are subject to recall bias. Second, because these data do
not include information on nonleisure-time physical activities, total activity may
be underestimated. Third, only the two most common activities the respondents
engaged in during the preceding month are reported. Finally, these data are limited
by coverage- and nonresponse-related errors.

Moderate-intensity physical activity has substantial health benefits
(1). Moderate-intensity activities include housework, childcare activities, occupational activity,
or walking for transportation, which may be more prevalent among women and
certain subgroups of the population. However, surveillance systems that primarily are
based on sports-related vigorous activities may miss a substantial portion of this type
of activity. Also, systems based on only two reported activities may miss less intense
or moderate-intensity activities. Public health programs usually encourage
participation in moderate-intensity rather than vigorous-intensity activities for sedentary
persons. Surveillance systems should be updated so that a broader range of physical
activities can be measured. A more extensive measurement system would
enable determination of whether the trends in this report are an accurate reflection of
physical activity trends in the United States.

References

US Department of Health and Human Services. Physical activity and health: report
of the Surgeon General. Atlanta, Georgia: US Department of Health and Human
Services, CDC, National Center for Chronic Disease Prevention and Health Promotion, 1996.

DisclaimerAll MMWR HTML versions of articles are electronic conversions from ASCII text
into HTML. This conversion may have resulted in character translation or format errors in the HTML version.
Users should not rely on this HTML document, but are referred to the electronic PDF version and/or
the original MMWR paper copy for the official text, figures, and tables.
An original paper copy of this issue can be obtained from the Superintendent of Documents,
U.S. Government Printing Office (GPO), Washington, DC 20402-9371; telephone: (202) 512-1800.
Contact GPO for current prices.

**Questions or messages regarding errors in formatting should be addressed to
mmwrq@cdc.gov.